What test can be performed to assess the association between change in nerve root compression and clinical outcome? 

The investigators also assessed clinical outcomes for the patients at 1 year. They defined a favorable outcome as a complete or nearly complete disappearance of symptoms on a patient-reported Likert scale for global perceived recovery. One of the paradoxes of sciatica is that sometimes patients perceive less pain even if MRI findings have  not changed. A comparison was made between the patient reported favorable outcome and change in the MRI assessment of extent of nerve root compression (1 yr. vs. baseline). The results were as follows:

Among 224 patients with a favorable outcome, nerve root compression had disappeared completely at 1 year for 169 patients, was present at 1 year but reduced from baseline for 39 patients, and was unchanged or increased from baseline for 16 patients. Among 43 patients with an unfavorable outcome, nerve root compression had disappeared completely at 1 year for 29 patients, was present at 1 year but reduced from baseline for 6 patients, and was unchanged or increased from baseline for 8 patients.